The present invention relates to a method of writing a file onto a tape, and more specifically to a method of writing a file onto a tape in a file system.
For example, as a mechanism for accessing data in a tape drive as a file in a file system, an LTFS (Linear Tape File System) is in practical use. In the LTFS, meta-information indicating where on a tape a data area constituting the file is, and the like is associated as index information to realize the file system. The mechanism enables direct access from an application program executed on a computer to a file in the tape drive.
The speed of writing data to a tape is determined by the standard of the tape drive. For example, in the case of an LTO-5 tape drive as one of the LTO standards, the data transfer rate is higher than that of normal hard disks. Although the maximum speed thereof when the data is uncompressed is about 140 MB/sec, the time to move the head is added. In addition to that, in the case of an LTFS, since it is necessary to store the above-mentioned index information together with data constituting a file and generate API calls (system calls), namely “open,” “write,” and “close,” for each file unit in the file system, it is noted that the data transfer rate (the speed of writing data to a tape) becomes further lower.
It is pointed out that this problem becomes pronounced particularly when a large number of small-sized files are written onto a tape in the LTFS. For example, as a result of a test in an LTO-6 tape drive, it is found that the data transfer rate (MB/sec) tends to become lower as the file size becomes smaller than 512 KB.
This reduction in transfer rate is considered to be mainly caused by the overhead due to API calls to “open” and “close” a file, the overhead due to updating of index information as a result of adding a file, or the like. Further, since the tape continues to run during interaction from when one file is closed until the next file is opened, the writing speed also needs to be reduced to make coordination, and this causes performance decline as well.